1. Field of the Invention
This invention relates to the field of cutting tools for plastic pipes and more particularly to the field of manually operated cutting tools with locking mechanisms that hold the jaws of the tool safely closed when not in use.
2. Discussion of the Background
Cutting tools for plastic pipes are widely used throughout the world and are an essential piece of equipment for virtually anyone who works with plastic pipes. In a typical design, two elongated members are pivotally connected together in a scissors-like manner. In operation, the handles of the tool can be manually manipulated to separate them and open the jaws of the tool to receive the plastic pipe to be cut. In doing so, the handles can be rubbed along the user's leg to separate them and open the tool's jaws or the user can extend his or her fingers to separate the handles. Once opened with the pipe received between the jaws of the tool, the handles can then be squeezed together to drive the edge of the knife blade on one of the jaws into the pipe. At the same time, the tool is normally swung relative to the pipe as the knife edge continues to be driven into the pipe until the pipe is eventually severed.
In other designs of such cutting tools, a spring or springs are provided to bias the handles apart and the jaws into an open position to receive the pipe. When a number of cuts are to be done, many users find it more efficient to have a spring-biased tool rather than one whose handles must be manually opened for each cut.
In both the manually operated and spring-biased designs, it is desirable to have locking mechanisms to secure the tool in a closed position with the jaws safely together when the tool is not in use. A very popular locking mechanism involves providing a bail on the end of one of the tool handles. In use, the tool can be manually closed to bring the handle ends together and the bail then pivoted over the end of the other handle. To unlock the tool, the bail can be either manually pivoted to release the other handle or rubbed against something to move it away from engagement with the other handle. Although simple and easy to operate, this locking arrangement has the disadvantage that the bail may be inadvertently struck and released as the tool is handled. This can occur because the bail is on the outside of the handle ends exposing it to being contacted and released unintentionally. If the tool is spring-biased toward its open position, the inadvertent release of the locking bail can then cause the tool to open, undesirably exposing the cutting blade of the tool. Other locking designs have the bails mounted on the inside of the handles but are somewhat complicated and expensive to make and can still be inadvertently released In contrast, the self-locking cutting tool of the present invention is relatively simple to operate and is less prone to being inadvertently released.